1. Field of the Invention
This invention relates to an imaging optical system for use in the objective lens of a microscope or the like, and particularly to an infinity system imaging optical system comprising two portions and forming the image of an object at infinity by a first lens portion movable along the optical axis for focus adjustment, and again forming this image at a predetermined location at a predetermined magnification by a second lens portion.
2. Related Background Art
This invention relates to the construction of a re-imaging lens (or a second objective lens or a collimator lens) when, in a so-called infinity system imaging optical system known in a microscope or the like, a first objective lens is moved in the direction of the optical axis for focus adjustment. The infinity system imaging optical system, as shown in FIG. 13 of the accompanying drawings, comprises a first objective lens G.sub.1 and a second objective lens G.sub.2, and forms the image of an object surface 0 at infinity by the first objective lens G.sub.1, and again forms that image at a predetermined magnification on the image plane I. The second objective lens in such an infinite system imaging optical system is known, for example, from Japanese Patent Publication No. 61-61650 or Japanese Laid-Open Patent Application No. 63-311222.
Now, in the conventional infinity system imaging optical system, focus adjustment is accomplished by the entire optical system being moved relative to an object, and any system in which focus adjustment is accomplished by only the first objective lens being moved has not yet been proposed.
Moreover, the conventional second objective lens is comprised of four lens units, as seen, for example, the above-mentioned Japanese Laid-Open Patent Application No. 63-311222.